Fuse



H. THOMMEN EIAL Jan. 28, 1941.

FUSE

Filed June 13, 1938 Patented Jan. 28, 194 1 I PATENT OFFICE FUSE Hans Thommen, Baden, 'andlians Muller, Ennetbaden, Switzerland, assignors to Aktiengeseli- Application June 1:, ms, Serial No. 213,340 In Germany June 16,1937 I 8 Claims. (Cl. zoo-1:1)

Ano'ther object of the present invention is to ..This invention relates in general to improvements in fuses for protecting high voltage electric circuits, and more particularly to a fuse of the type in which the fuse element is embedded I in a pulverulent insulating material.

{iigh voltagefuses are well known in whicha fuse element shaped as a wire or a plurality of parallel wires is embedded in a pulveriilent im sulating material such as fine sand. The fuse 10 wires utilized in hlgh voltage fuses must'be of small diameter to avoid occurrence of excessive local pressures upon operation of the fuse, and these wires, being of relatively soft metal, are easily stretched or even broken. It has been a proposed to fasten the wires between-the fuse terminals without supporting them at any intermediate point. This construction presents'the disadvantage that some of the wires may be broken when the fuse is filled with sand, and

, this defect cannot be conveniently detected as 0 8 as some of the wires remain unbroken. vThe wires may also be helically wound on a cylindrical insulator provided with suitabl helical grooves. The wires are then well supported, but a continuous coating of conductive material from the wires may be deposited on the insulator upon operation of the fuse resulting in current leakage between the fuse terminals.

These disadvantages may be avoided by supporting each fuse wire at spaced points intermediate the fuse terminals by helically winding the wires on a star shaped rod insulator for example. when a plurality of parallel wires are necessary, these wires are preferably obtained by looping a single piece of conductor back and forth between the fuse terminals. One of the wires may be used to maintain an indicator out of operation indicating position, and the indicator wire is preferably made longer than the 0 other wires to preclude any premature release of the indicator. A relatively large amount of heat is frequently evolved in large capacity fuseswhich are therefore preferably provided with a passage for the flow of cooling fluid therethrouflh. I

It is therefore one of the objects of the present I invention to provide a fuse of the type containing pulverulent insulating material in which each fuse wire is supported at spaced points inter-. mediate the fuse terminals. Another object of the pment invention is to provide a fuse of the type containingpulverulent insulating material in which one of a plurality of parallel fuse wires is utilized to'control an up g eration indicator.

provide a fuse of the type containing pulverulent insulating material in which a relatively large amount of heat may be dissipated without exces sively raising the temperature of the fuse.

Objects and advantages other than those above described will be apparent from the following descrlption when read in connection with the accoinpanying drawing, in which:

,Fig. 1 is a longitudinal cross section through and . Fig. 2 is a cross section taken on plane II-II through the embodiment illustrated in Fig.- 1 from which the filling of pulverulent insulating material is removed.

Referring more particularly to the drawing by characters of reference, reference numeral 6 deiignates'an insulating fuse casing on which are mounted a pair of apertured terminal structures generally designated by I, 8. Casing 6 preferably consists of a hollow cylinder of porcelain. The two terminals are generally similar to one another in construction and comprise suitable contact members such as knife blade contacts 9, ll, adapted to be inserted in a suitable holder (not shown) .for connecting the fuse in an electric circuit in the usual known manner. Blades 9, II are assembled on casing 6 through internally flanged metal tubes or ferrules l2, l3, to which the blades are riveted or otherwise fastened. Each ferrule is slipped over one endof casing 8 and is maintained in position thereon by any suitable means. For example, the casing may be provided with recesses .15, into which solder may be run through apertures drilled in the ferrules. The parts are preferably preheated and the ferrules are coated with a suitable flux or even tinned before introducing the solder,

which forms lugs integral with the ferrules preventing their displacement relative to casing 6.

The terminals further comprise a pair of washem I, II, resiliently maintained in contact with- 'Or target 28 mounted on casing 6 through the elements of terminal 8 and tending to protrude through the aperture of cap 22 under the joint action of gravity and of a spring 2. Washers IO, l1 are provided with slotted tubular extensions fitted around a pair of apertured caps 16, 21 and urged in contact therewith by springs 28, 5 29. Cap 21 is provided with suitable ears 3!, 33 for fastening the ends of a conductor serving as fuse wire and caps 26 and 21 are flanged to form rows of hooks 34, 35 between which the conductor may b looped to form a plurality of parallel fuse wires. If it is desired to utilize an odd number of fuse wires, ears similar to 32 on cap 21 may be utilized on cap 26.

Caps 26, 21 are cemented or otherwise fastened to the ends of a rod insulator 3! arranged in casing 6 and maintained between terminals 1 and 8 by the caps, which form part of the terminals. Insulator 311 is a hollow rod of star shaped. cross section and the bore thereof is alined with the apertures of caps 2t], 22, of caps as, 21, and of indicator 28 to define a passage for the flow of cooling fluid through the fuse. in general, sufliclent cooling of the fuse will be obtained by allowing atmopheric air to circulate through the passage under natural draft caused by heating of the air duringits travel through the passage.

The fuse element is mounted in casing 8 for interconnecting terminals 1 and 8, and consists of a plurality of parallel fuse wires 36, 31, I! and 30 39 embedded in a body of pulverulent insulating material 4| such as fine sand contained in casing 6 between the casing and insulator 3|. It is generally necessary to utilize a plurality of parallel fuse wires to obtain a fuse element having the desired current carrying capacity because the diameter of the wires should not exceed one-third of a millimeter to limit the amount of metal vapor produced at any point by fusion of a re and thus to limit the maxi- 40 mum pressure eveloped in the fuse. The wires are most conveniently obtained from a single piece of fusible conductor looped between the fuse terminals. -WiresIi, 31 and a are of sub-- stantially uniform predetermined length and are 45 embedded in sand over their entire length. Wire 39, which is'longer than the other wires, is embedded in sand ll over a length substantially equal to the length ofthe remaining wires. Wire 3! however extends out of thesand throughan 50 insulating tube 42 into engagement with indicator 23 to maintain the indicator out of operation indicating position. Insulator 3! is provided with a plurality of interleaved discontinuous helical grooves to accommodate an equal 55 number of fuse wires, although the fuse wires actually used may be in any number not exceeding the numberofgrooves. The wires are wound around insulator 3| in interleaved helical paths'partly in the grooves and partly in sand so between the successive groove portions. In this manner the length of the fuse can be made considerably less than the length of the fuse wires and thecostofthefuseandofthe fuse holdermay be considerably reduced. The 66 fuse wires are discontinuously supported be tween terminals 1. and I in order that they may be completely surrounded by sand between the spaced points of support of the wires on insulator 1|. .The wires are accordingly wound sufficiently 70 obtain spacing of the wire portions intermediate the spaced points ofsupport thereofoninsulator il'fromthe'insulatoracross the concave portions thereof. The volume of sand confined between the wires and the concave ll portions of the innilator prevents deposition around the insulator 3| to form wire 31.

of a continuous coating of conductor material from the wire on the insulator surface between the spaced points of support of the wires upon fusing thereof. A coating is indeed deposited in the insulator grooves with which the wires are in contact, but the sand present between the wires and the concave insulator surfaces prevents the deposition on the insulator of a continuous coating extending between terminals 1 and 8,

which continuous coating would cause current leakage between the terminals.

The distance between adjacent parallel wires venting excessive heat concentration and pro-' duction of excessive pressures in the fuse casing. The distance between successive turns of the group of wires is preferably made greater than the distance between adjacent wires to positively preclude establishment of a direct are between the terminals from turn to turn of the fuse wires upon operation of the fuse.

To assemble the fuse, a piece of "fusible conductor of suitable length is selected and one end thereof is anchored under ear 32 of cap 21. The conductor is passed between two of hooks 85 and is helically wound around insulator 3| to form wire a. The conductor is then slipped over one of hooks I4 and helically wound a second time The conductor is thus looped back and forth between the terminals to form as many wires as are required. The last wire 39 is not brought back to ear 3!, but is instead threaded through tube 42 and looped around indicator 23. The indicator comprises a lower tubular portion which is slotted so that the wire may rest on the upper globular portion of the indicator. The indicator is pressed upward by hand against the action of spring 24 until the indicator abuts against cap 21. Wire ll is then pulled tightly around the indicator and the end-thereof in anchored under ear 3:. Washer I1 is then mounted on cap 21 and the insulator is inserted into casing 61 Spring 19 is abutted against washer l1 and is held in place by means of cap 22 which is fastened on ferrule II through bayonet mounting Ill. Band is then poured into casing 6 to fill the space between the casing and insulator 3| to a level slightly above hooks I. A layer of resilient material 43, such as rock wool, is then disposed above the sand up to approximately the upper edge of ferrule II. Washer I6 is slipped over cap 28 and brought into contact with the edge of ferrule l2, thuseompressing the rock wool and holding sand ll immovable in casing 6. Spring I8 is laid on washer l0 and is compressed by cap 2| which is fastened on ferrule I! through its bayonet moimting. The fuse is thus completely assembled and may .be-put in service by inserting knife sistance and carries a slightly lower current than each of the remaining wires. If the current through the fuse reaches or exceeds the value at which the fuse should operate, wires 96, 31 and 38 fuse first substantially simultaneously. The fused material is vaporized and the metallic vapor is oxidized by the air contained between the sand grains and diffuses into the sand surrounding the wires. The oxidized metallic vapor settles on the sand grains which are thus coated with a layer of substantially non-conductive metallic oxide. Some molten metal from the wire portions located in the grooves of insulator 3| may form a conductive layer on the surface of the grooves but this layer is interrupted by the concave portions of insulator 3| and therefore cannot carry any leakage current between the terminals of the fuse.

Wire 39, receiving less current than the other wires, will fuse at a somewhat later moment and even if the total current merely reaches the value suihcient to cause wires 36, 31 and 39 to fuse, wire 39 will certainly fuse after the other wires have fused when the entire fuse current is carried by wire 39. The portion of wire 39 embedded in sand, which is thus insulated against heat transmission, fuses while the portion thereof enclosed in cap 22, which may radiate heat through the surrounding air, remains unaffected. The portion of wire 39 looped around indicator 23' is then no longer held taut and releases the indicator. Spring 24 causes the indicator to project through the aperture of cap 22 to indicate operation of the fuse. The sequential fusing of wires 38, '31, 39 and of wire 39 insures that the indicator will not be released except uponflow of current sufficient to fuse all wires. When the fuse has operated, it may be disassembled, the sand and the unfused ends of the wires removed, and the fuse reas-, sembled with a new fusible conductor and a new sand filling in the manner above set forth.

Although but one embodiment of the present invention has been illustrated and described, it

will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention or from the spirit of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A fuse comprising a pair of terminals, a rod insulator of star shaped cross section arranged between said terminals, and a fuse element interconnecting said terminals and comprising a group of parallel fuse wires wound in spaced interleaved helical paths around said insulator, the distance between successive turns of the group of wires being greater than the distance between adjacent parallel wires.

2. A fuse comprising a pair of terminals, a fuse element consisting of a single piece of fusible conductor looped between said terminals to form a plurality of parallel fuse wires, and an indicator for indicating operation of the fuse, said indicator being maintained out of operation indicating position by a single one of said wires.

3. A fuse comprising a pair of terminals, an in-. dicator for indicating operation of the fuse, and a fuse element consisting'of a single piece of fusible conductor looped between said terminals to form a plurality of parallel fuse wires, one of said wires being longer than the remainder of said wires and serving to maintain said indicator out of operation indicating position.

4. A fuse comprlsnig an insulat ng casing.

pair of terminals mounted on said casing, an indicator mounted onsaid casing for indicating operation of the fuse, a body of pulverulent insulating material contained in said casing, and a fuse element consisting of a single piece of fusible conductor looped between said terminals to form a plurality of parallel fuse wires of predetermined length embedded in said material and anotherv wire embedded in said material over a length substantially equal to said predetermined length and extending out of said material into engagement with said indicator to maintain said indicator out of operation indicating position.

5. A fuse comprising an insulating casing, a pair of terminals mounted on said casing, a rod insulator of star shaped cross section arranged in said casing between said terminals, an indicator mounted on said casing for indicating operation of the fuse, a body of pulverulent insulating material contained between said casing and said insulator, and a fuse element consisting of a single piece of fusible conductor looped'between said around said insulator and embedded in said ma-' terial, one of said wires extending out of said material into engagement with said indicator to maintain said indicator out of operation indicating position.

6. A fuse comprising an insulating casing, a pair of apertured terminals mounted on said casing, a hollow rod insulator of star shaped cross section arranged in saidcasing, a fuse element interconnecting said terminals and helically wound around said insulator, and a body of pulverulent insulating material in said casing in exclusive contact with said element between the points of contact of said element with said insulator, said insulator and said terminals defining a passage for the flow of cooling fluid through the fuse.

'1. A fuse comprising an insulating casing, a pair of .apertured terminals mounted on said casing, a. hollow rod insulator of star shaped cross section arranged in said casing between said terminals, a hollow indicator arranged to extend through an aperture of one of said terminals to indicate operation of the fuse, a body of pulverulent insulating material contained between said casing and said insulator, and a fuse element comprising a plurality of parallel wires. interconnecting said terminals helically wound around said insulator and embedded in said material, one

of said wires extending out of said material into engagement with said indicator to maintain said indicator out of operation indicating position,

said terminals, insulator and indicator defining a passage for the flow of cooling fluid through the fuse.

8. A fuse comprising an insulating casing, a

pair of terminals mounted on said casing, a rod insulator of star shaped cross section arranged in said casing, a body of pulvemlent insulating material contained between said casing and said insulator, and a fuse element interconnecting said terminalsand comprising a plurality of parallel wires wound in spaced interleaved helical paths around said insulator, the spacing of said wires comprising means for confining .to a separate 

